Photoresist compositions are used in microlithography processes for making miniaturized electronic components such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The photoresist coated on the substrate is next subjected to an image-wise exposure to radiation.
The radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation exposed (positive photoresist) or the unexposed areas of the photoresist (negative photoresist).
Positive working photoresists when they are exposed image-wise to radiation have those areas of the photoresist composition exposed to the radiation become more soluble to the developer solution while those areas not exposed remain relatively insoluble to the developer solution. Thus, treatment of an exposed positive-working photoresist with the developer causes removal of the exposed areas of the coating and the formation of a positive image in the photoresist coating. Again, a desired portion of the underlying surface is uncovered.
Negative working photoresists when they are exposed image-wise to radiation, have those areas of the photoresist composition exposed to the radiation become insoluble to the developer solution while those areas not exposed remain relatively soluble to the developer solution. Thus, treatment of a non-exposed negative-working photoresist with the developer causes removal of the unexposed areas of the coating and the formation of a negative image in the photoresist coating. Again, a desired portion of the underlying surface is uncovered.
Photoresist resolution is defined as the smallest feature which the photoresist composition can transfer from the photomask to the substrate with a high degree of image edge acuity after exposure and development. In many leading edge manufacturing applications today, photoresist resolution on the order of less than 100 nm is necessary. In addition, it is almost always desirable that the developed photoresist wall profiles be near vertical relative to the substrate, photoresist images are free of residues, have good depth of focus and the photoresist have good long term and short term stability. Good lithographic properties are important for the photoresist. Such demarcations between developed and undeveloped areas of the photoresist coating translate into accurate pattern transfer of the mask image onto the substrate. This becomes even more critical as the push toward miniaturization reduces the critical dimensions on the devices.
The trend towards the miniaturization of semiconductor devices has led to the use of new photoresists that are sensitive at lower and lower wavelengths of radiation and has also led to the use of sophisticated multilevel systems, such as antireflective coatings, to overcome difficulties associated with such miniaturization.
Photoresists sensitive to short wavelengths, less than about 300 nm, are often used where subhalfmicron geometries are required. Particularly preferred are deep uv photoresists sensitive at below 200 nm, e.g. 193 nm and 157 nm, comprising non-aromatic polymers, a photoacid generator, optionally a dissolution inhibitor, and solvent.
The use of highly absorbing antireflective coatings in photolithography is a useful approach to diminish the problems that result from back reflection of radiation from highly reflective substrates. The bottom antireflective coating is applied on the substrate and then a layer of photoresist is applied on top of the antireflective coating. The photoresist is exposed imagewise and developed. The antireflective coating in the exposed area is then typically dry etched using various etching gases, and the photoresist pattern is thus transferred to the substrate. In cases where the photoresist does not provide sufficient dry etch resistance, underlayers or antireflective coatings for the photoresist that are highly etch resistant are preferred, and one approach has been to chemically vapor deposit layers with high content of carbon. Carbon is known to be highly etch resistant for gases used to etch the layers beneath the antireflective coating. However, the deposition of carbon typically requires a vapor deposition technique utilizing expensive vacuum equipment, and therefore is not highly desirable. An organic spin castable antireflective coating which incorporates as high content as possible of carbon into these underlayers is one preferred alternative. Antireflective coatings comprising a polymer and a crosslinking agent comprising a high concentration of carbon are highly desirable. Additionally, the antireflective coating composition which has a minimal concentration of oxygen, nitrogen, halogen, and other noncarbon constituents is desirable, and aromatic moieties, such as phenyl, are very desirable.
The present invention provides for a novel organic spin castable antireflective coating composition for a photoresist, where the composition comprises a crosslinkable polymer which is absorbing and a polymeric crosslinker capable of crosslinking with the crosslinkable polymer in the presence of an acid. The novel antireflective coating is spin castable on the substrate. The antireflective composition of the present invention provides for an underlayer or antireflective coating with high carbon content, and therefore a high degree of etch resistance, that is, a low etch rate relative to the substrate. Such antireflective coatings also function as hard masks for etching the substrate, where the hard mask prevents the substrate from being etched by the etching gases. An antireflective coating composition for high etch rate is disclosed in US 2001/0034427 and U.S. Pat. No. 7,033,729.
The invention also provides for a process for using the antireflective coating to form an image using the novel composition. The novel composition is useful for imaging photoresists which are coated directly over the novel antireflective coating composition or with intervening layers, and also for etching the substrate. The novel composition enables a good image transfer from the photoresist to the substrate, and also has good absorption characteristics to prevent reflective notching and line width variations or standing waves in the photoresist. Additionally, substantially no intermixing is present between the antireflective coating and the film coated over this coating. The antireflective coating also has good solution stability and forms films with good coating quality, the latter being particularly advantageous for lithography.